Decreased expression of natriuretic peptides associated with lipid accumulation in cardiac ventricle of obese mice

Diastolic Dysfunction with Normal Ejection Fraction and Reduced Heart Rate in Mice Expressing Human Growth Hormone and Displaying Signs of Growth Hormone Insufficiency

Growth hormone (GH) signaling is essential for heart development. Both GH deficiency and excess raise cardiovascular risk. Human (h) and mouse (m) GH differ structurally and functionally: hGH binds both the GH receptor (GHR) and prolactin receptor (PRLR), whereas mGH binds only GHR; thus, there is the potential for differential effects. We generated transgenic (hGH-TG) mice that produce pituitary hGH in response to hypothalamic signaling. These mice grow at the same rate as mGH-expressing wild-type (mGH-WT) mice but are smaller and have higher body fat. Echocardiography was used here to compare hGH-TG and mGH-WT mouse hearts. Male hGH-TG mice show a 48% lower left ventricular mass, 36% lower stroke volume, and 48% reduced cardiac output, resembling GH deficiency. Diastolic dysfunction, restrictive ventricular filling, and lower heart rate are suggested in hGH-TG mice. No significant differences in ejection fraction or fractional shortening were observed, even after high-fat diet (HFD) stress. HFD did not affect RNA markers of cardiac damage, although a possible association between B-type natriuretic peptide RNA levels and heart rate was detected. These observations suggest that diastolic dysfunction related to hGH and/or low GH might be offset by a lower heart rate, while structural changes precede functional effects.

From Beats to Metabolism: the Heart at the Core of Interorgan Metabolic Cross Talk

The heart, once considered a mere blood pump, is now recognized as a multifunctional metabolic and endocrine organ. Its function is tightly regulated by various metabolic processes, at the same time it serves as an endocrine organ, secreting bioactive molecules that impact systemic metabolism. In recent years, research has shed light on the intricate interplay between the heart and other metabolic organs, such as adipose tissue, liver, and skeletal muscle. The metabolic flexibility of the heart and its ability to switch between different energy substrates play a crucial role in maintaining cardiac function and overall metabolic homeostasis. Gaining a comprehensive understanding of how metabolic disorders disrupt cardiac metabolism is crucial, as it plays a pivotal role in the development and progression of cardiac diseases. The emerging understanding of the heart as a metabolic and endocrine organ highlights its essential contribution to whole body metabolic regulation and offers new insights into the pathogenesis of metabolic diseases, such as obesity, diabetes, and cardiovascular disorders. In this review, we provide an in-depth exploration of the heart's metabolic and endocrine functions, emphasizing its role in systemic metabolism and the interplay between the heart and other metabolic organs. Furthermore, emerging evidence suggests a correlation between heart disease and other conditions such as aging and cancer, indicating that the metabolic dysfunction observed in these conditions may share common underlying mechanisms. By unraveling the complex mechanisms underlying cardiac metabolism, we aim to contribute to the development of novel therapeutic strategies for metabolic diseases and improve overall cardiovascular health.

Exploring the Mechanistic Link Between Obesity and Heart Failure

PURPOSE OF REVIEW

Among subtypes of cardiovascular disease, obesity has a potent and unique association with heart failure (HF) that is unexplained by traditional cardiovascular risk mediators. The concomitant rise in the prevalence of obesity and HF necessitates better understanding of their relationship to develop effective prevention and treatment strategies. The purpose of this review is to provide mechanistic insight regarding the link between obesity and HF by elucidating the direct and indirect pathways linking the two conditions.

RECENT FINDINGS

Several direct pathophysiologic mechanisms contribute to HF risk in individuals with excess weight, including hemodynamic alterations, neurohormonal activation, hormonal effects of dysfunctional adipose tissue, ectopic fat deposition with resulting lipotoxicity and microvascular dysfunction. Obesity further predisposes to HF indirectly through causal associations with hypertension, dyslipidemia, and most importantly, diabetes via insulin resistance. Low levels of physical activity and fitness further influence HF risk in the context of obesity. These various processes lead to myocardial injury and cardiac remodeling that are reflected by abnormalities in cardiac biomarkers and cardiac function on myocardial imaging. Understanding and addressing obesity-associated HF is a pressing clinical and public health challenge which can be informed by a deeper understanding of the complex pathways linking these two conditions together.

Deletion of the Npr3 gene increases severity of acute lung injury in obese mice

Previous studies have shown that atrial natriuretic peptide (ANP) attenuates agonist-induced pulmonary edema and that this effect may be mediated in part by the ANP clearance receptor, natriuretic peptide receptor-C (NPR-C). Obesity has been associated with lower plasma ANP levels due to increased expression of NPR-C, and with decreased severity of acute lung injury (ALI). Therefore, we hypothesized that increased expression of NPR-C may attenuate ALI severity in obese populations. To test this, we examined ALI in Npr3 wild-type (WT) and knockout (KO) mice fed normal chow (NC) or high-fat diets (HFD). After 12 weeks, ALI was induced with intra-tracheal administration of Pseudomonas aeruginosa strain 103 (PA103) or saline. ALI severity was determined by lung wet-to-dry ratio (W/D) along with measurement of cell count, protein levels from bronchoalveolar lavage fluid (BALF), and quantitative polymerase chain reaction was performed on whole lung to measure cytokine/chemokine and Npr3 mRNA expression. ANP levels were measured from plasma. PA103 caused ALI as determined by significant increases in W/D, BALF protein concentration, and whole lung cytokine/chemokine expression. PA103 increased Npr3 expression in the lungs of wild-type (WT) mice regardless of diet. There was a nonsignificant trend toward increased Npr3 expression in the lungs of WT mice fed HFD versus NC. No differences in ALI were seen between Npr3 knockout (KO) mice and WT-fed NC, but Npr3 KO mice fed HFD had a significantly greater W/D and BALF protein concentration than WT mice fed HFD. These findings support the hypothesis that Npr3 may help protect against ALI in obesity.

Type II Transmembrane Serine Proteases as Modulators in Adipose Tissue Phenotype and Function

Adipose tissue is a crucial organ in energy metabolism and thermoregulation. Adipose tissue phenotype is controlled by various signaling mechanisms under pathophysiological conditions. Type II transmembrane serine proteases (TTSPs) are a group of trypsin-like enzymes anchoring on the cell surface. These proteases act in diverse tissues to regulate physiological processes, such as food digestion, salt-water balance, iron metabolism, epithelial integrity, and auditory nerve development. More recently, several members of the TTSP family, namely, hepsin, matriptase-2, and corin, have been shown to play a role in regulating lipid metabolism, adipose tissue phenotype, and thermogenesis, via direct growth factor activation or indirect hormonal mechanisms. In mice, hepsin deficiency increases adipose browning and protects from high-fat diet-induced hyperglycemia, hyperlipidemia, and obesity. Similarly, matriptase-2 deficiency increases fat lipolysis and reduces obesity and hepatic steatosis in high-fat diet-fed mice. In contrast, corin deficiency increases white adipose weights and cell sizes, suppresses adipocyte browning and thermogenic responses, and causes cold intolerance in mice. These findings highlight an important role of TTSPs in modifying cellular phenotype and function in adipose tissue. In this review, we provide a brief description about TTSPs and discuss recent findings regarding the role of hepsin, matriptase-2, and corin in regulating adipose tissue phenotype, energy metabolism, and thermogenic responses.

Diabetes disturbs functional adaptation of the remote myocardium after ischemia/reperfusion

Diabetes mellitus type 2 is associated with adverse clinical outcome after myocardial infarction. To better understand the underlying causes we here investigated sarcomere protein function and its calcium-dependent regulation in the non-ischemic remote myocardium (RM) of diabetic mice (db/db) after transient occlusion of the left anterior descending coronary artery. Before and 24 h after surgery db/db and non-diabetic db/+ underwent magnetic resonance imaging followed by histological and biochemical analyses of heart tissue. Intracellular calcium transients and sarcomere function were measured in isolated cardiomyocytes. Active and passive force generation was assessed in skinned fibers and papillary muscle preparations. Before ischemia and reperfusion (I/R), beat-to-beat calcium cycling was depressed in diabetic cardiomyocytes. Nevertheless, contractile function was preserved owing to increased myofilament calcium sensitivity and higher responsiveness of myocardial force production to β-adrenergic stimulation in db/db compared to db/+. In addition, protein kinase C activity was elevated in db/db hearts leading to strong phosphorylation of the titin PEVK region and increased titin-based tension of myofilaments. I/R impaired the function of whole hearts and RM sarcomeres in db/db to a larger extent than in non-diabetic db/+, and we identified several reasons. First, the amplitude and the kinetics of cardiomyocyte calcium transients were further reduced in the RM of db/db. Underlying causes involved altered expression of calcium regulatory proteins. Diabetes and I/R additively reduced phospholamban S16-phosphorylation by 80% (P < 000.1) leading to strong inhibition of the calcium ATPase SERCA2a. Second, titin stiffening was only observed in the RM of db/+, but not in the RM of db/db. Finally, db/db myofilament calcium sensitivity and force generation upon β-adrenergic stimulation were no longer enhanced over db/+ in the RM. The findings demonstrate that impaired cardiomyocyte calcium cycling of db/db hearts is compensated by increased myofilament calcium sensitivity and increased titin-based stiffness prior to I/R. In contrast, sarcomere function of the RM 24 h after I/R is poor because both these compensatory mechanisms fail and myocyte calcium handling is further depressed.

Supplementation with the Prebiotic High-Esterified Pectin Improves Blood Pressure and Cardiovascular Risk Biomarker Profile, Counteracting Metabolic Malprogramming

Supplementation with the prebiotic pectin is associated with beneficial health effects. We aimed to characterize the cardioprotective actions of chronic high-esterified pectin (HEP) supplementation (10%) in a model of metabolic malprogramming in rats, prone to obesity and associated disorders: the progeny of mild calorie-restricted dams during the first half of pregnancy. Results show that pectin supplementation reverses metabolic malprogramming associated with gestational undernutrition. In this sense, HEP supplementation improved blood pressure, reduced heart lipid content, and regulated cardiac gene expression of atrial natriuretic peptide and lipid metabolism-related genes. Moreover, it caused an elevation in circulating levels of fibroblast growth factor 21 and a higher expression of its co-receptor β-klotho in the heart. Most effects are correlated with the gut levels of beneficial bacteria promoted by HEP. Therefore, chronic HEP supplementation shows cardioprotective actions, and hence, it is worth considering as a strategy to prevent programmed cardiometabolic alterations.

Role of natriuretic peptides in the cardiovascular-adipose communication: a tale of two organs

Natriuretic peptides have long been known for their cardiovascular function. However, a growing body of evidence emphasizes the role of natriuretic peptides in the energy metabolism of several substrates in humans and animals, thus interrelating the heart, as an endocrine organ, with various insulin-sensitive tissues and organs such as adipose tissue, muscle skeletal, and liver. Adipose tissue dysfunction is associated with altered regulation of the natriuretic peptide system, also indicated as a natriuretic disability. Evidence points to a contribution of this natriuretic disability to the development of obesity, type 2 diabetes mellitus, and cardiometabolic complications; although the causal relationship is not fully understood at present. However, targeting the natriuretic peptide pathway may improve metabolic health in obesity and type 2 diabetes mellitus. This review will focus on the current literature on the metabolic functions of natriuretic peptides with emphasis on lipid metabolism and insulin sensitivity. Natriuretic peptide system alterations could be proposed as one of the linking mechanisms between adipose tissue dysfunction and cardiovascular disease.

Heart failure with preserved ejection fraction in humans and mice: embracing clinical complexity in mouse models

Heart failure (HF) with preserved ejection fraction (HFpEF) is a multifactorial disease accounting for a large and increasing proportion of all clinical HF presentations. As a clinical syndrome, HFpEF is characterized by typical signs and symptoms of HF, a distinct cardiac phenotype and raised natriuretic peptides. Non-cardiac comorbidities frequently co-exist and contribute to the pathophysiology of HFpEF. To date, no therapy has proven to improve outcomes in HFpEF, with drug development hampered, at least partly, by lack of consensus on appropriate standards for pre-clinical HFpEF models. Recently, two clinical algorithms (HFA-PEFF and H₂FPEF scores) have been developed to improve and standardize the diagnosis of HFpEF. In this review, we evaluate the translational utility of HFpEF mouse models in the context of these HFpEF scores. We systematically recorded evidence of symptoms and signs of HF or clinical HFpEF features and included several cardiac and extra-cardiac parameters as well as age and sex for each HFpEF mouse model. We found that most of the pre-clinical HFpEF models do not meet the HFpEF clinical criteria, although some multifactorial models resemble human HFpEF to a reasonable extent. We therefore conclude that to optimize the translational value of mouse models to human HFpEF, a novel approach for the development of pre-clinical HFpEF models is needed, taking into account the complex HFpEF pathophysiology in humans.

Sphingolipid imbalance and inflammatory effects induced by uremic toxins in heart and kidney cells are reversed by dihydroceramide desaturase 1 inhibition

Non-dialysable protein-bound uremic toxins (PBUTs) contribute to the development of cardiovascular disease (CVD) in chronic kidney disease (CKD) and vice versa. PBUTs have been shown to alter sphingolipid imbalance. Dihydroceramide desaturase 1 (Des1) is an important gatekeeper enzyme which controls the non-reversible conversion of sphingolipids, dihydroceramide, into ceramide. The present study assessed the effect of Des1 inhibition on PBUT-induced cardiac and renal effects in vitro, using a selective Des1 inhibitor (CIN038). Des1 inhibition attenuated hypertrophy in neonatal rat cardiac myocytes and collagen synthesis in neonatal rat cardiac fibroblasts and renal mesangial cells induced by the PBUTs, indoxyl sulfate and p-cresol sulfate. This is at least attributable to modulation of NF-κB signalling and reductions in β-MHC, Collagen I and TNF-α gene expression. Lipidomic analyses revealed Des1 inhibition restored C16-dihydroceramide levels reduced by indoxyl sulfate. In conclusion, PBUTs play a critical role in mediating sphingolipid imbalance and inflammatory responses in heart and kidney cells, and these effects were attenuated by Des1 inhibition. Therefore, sphingolipid modifying agents may have therapeutic potential for the treatment of CVD and CKD and warrant further investigation.

Low-intensity pulsed ultrasound ameliorates cardiac diastolic dysfunction in mice: a possible novel therapy for heart failure with preserved left ventricular ejection fraction

AIMS

Heart failure with preserved left ventricular ejection fraction (HFpEF) is a serious health problem worldwide, as no effective therapy is yet available. We have previously demonstrated that our low-intensity pulsed ultrasound (LIPUS) therapy is effective and safe for angina and dementia. In this study, we aimed to examine whether the LIPUS therapy also ameliorates cardiac diastolic dysfunction in mice.

METHODS AND RESULTS

Twelve-week-old obese diabetic mice (db/db) and their control littermates (db/+) were treated with either the LIPUS therapy [1.875 MHz, 32 cycles, Ispta (spatial peak temporal average intensity) 117-162 mW/cm2, 0.25 W/cm2] or placebo procedure two times a week for 4 weeks. At 20-week-old, transthoracic echocardiography and invasive haemodynamic analysis showed that cardiac diastolic function parameters, such as e', E/e', end-diastolic pressure-volume relationship, Tau, and dP/dt min, were all deteriorated in placebo-treated db/db mice compared with db/+ mice, while systolic function was preserved. Importantly, these cardiac diastolic function parameters were significantly ameliorated in the LIPUS-treated db/db mice. We also measured the force (F) and intracellular Ca2+ ([Ca2+]i) in trabeculae dissected from ventricles. We found that relaxation time and [Ca2+]i decay (Tau) were prolonged during electrically stimulated twitch contractions in db/db mice, both of which were significantly ameliorated in the LIPUS-treated db/db mice, indicating that the LIPUS therapy also improves relaxation properties at tissue level. Functionally, exercise capacity was also improved in the LIPUS-treated db/db mice. Histologically, db/db mice displayed progressed cardiomyocyte hypertrophy and myocardial interstitial fibrosis, while those changes were significantly suppressed in the LIPUS-treated db/db mice. Mechanistically, western blot showed that the endothelial nitric oxide synthase (eNOS)-nitric oxide (NO)-cGMP-protein kinase G (PKG) pathway and Ca2+-handling molecules were up-regulated in the LIPUS-treated heart.

CONCLUSIONS

These results indicate that the LIPUS therapy ameliorates cardiac diastolic dysfunction in db/db mice through improvement of eNOS-NO-cGMP-PKG pathway and cardiomyocyte Ca2+-handling system, suggesting its potential usefulness for the treatment of HFpEF patients.

Sacubitril/valsartan inhibits obesity-associated diastolic dysfunction through suppression of ventricular-vascular stiffness

OBJECTIVE

Cardiac diastolic dysfunction (DD) and arterial stiffness are early manifestations of obesity-associated prediabetes, and both serve as risk factors for the development of heart failure with preserved ejection fraction (HFpEF). Since the incidence of DD and arterial stiffness are increasing worldwide due to exponential growth in obesity, an effective treatment is urgently needed to blunt their development and progression. Here we investigated whether the combination of an inhibitor of neprilysin (sacubitril), a natriuretic peptide-degrading enzyme, and an angiotensin II type 1 receptor blocker (valsartan), suppresses DD and arterial stiffness in an animal model of prediabetes more effectively than valsartan monotherapy.

METHODS

Sixteen-week-old male Zucker Obese rats (ZO; n = 64) were assigned randomly to 4 different groups: Group 1: saline control (ZOC); Group 2: sacubitril/valsartan (sac/val; 68 mg•kg-1•day-1; ZOSV); Group 3: valsartan (31 mg•kg-1•day-1; ZOV) and Group 4: hydralazine, an anti-hypertensive drug (30 mg•kg-1•day-1; ZOH). Six Zucker Lean (ZL) rats that received saline only (Group 5) served as lean controls (ZLC). Drugs were administered daily for 10 weeks by oral gavage.

RESULTS

Sac/val improved echocardiographic parameters of impaired left ventricular (LV) stiffness in untreated ZO rats, without altering the amount of food consumed or body weight gained. In addition to improving DD, sac/val decreased aortic stiffness and reversed impairment in nitric oxide-induced vascular relaxation in ZO rats. However, sac/val had no impact on LV hypertrophy. Notably, sac/val was more effective than val in ameliorating DD. Although, hydralazine was as effective as sac/val in improving these parameters, it adversely affected LV mass index. Further, cytokine array revealed distinct effects of sac/val, including marked suppression of Notch-1 by both valsartan and sac/val, suggesting that cardiovascular protection afforded by both share some common mechanisms; however, sac/val, but not val, increased IL-4, which is increasingly recognized for its cardiovascular protection, possibly contributing, in part, to more favorable effects of sac/val over val alone in improving obesity-associated DD.

CONCLUSIONS

These studies suggest that sac/val is superior to val in reversing obesity-associated DD. It is an effective drug combination to blunt progression of asymptomatic DD and vascular stiffness to HFpEF development in a preclinical model of obesity-associated prediabetes.

Sirtuin1 Role in the Melatonin Protective Effects Against Obesity-Related Heart Injury

Obesity is a worldwide epidemic disease that induces important structural and functional changes to the heart and predisposes a patient to devastating cardiac complications. Sirtuin1 (SIRT1) has been found to have roles in regulating cardiac function, but whether it can help in cardioprotection is not clear. The aim of the present study was to determine whether melatonin, by modulating SIRT1 and in turn mitochondria signaling, may alleviate obesity-induced cardiac injuries. We investigated 10 lean control mice and 10 leptin-deficient obese mice (ob/ob) orally supplemented with melatonin for 8 weeks, as well as equal numbers of age-matched lean and ob/ob mice that did not receive melatonin. Hearts were evaluated using multiple parameters, including biometric values, morphology, SIRT1 activity and expression of markers of mitochondria biogenesis, oxidative stress, and inflammation. We observed that ob/ob mice experienced significant heart hypertrophy, infiltration by inflammatory cells, reduced SIRT1 activity, altered mitochondrial signaling and oxidative balance, and overexpression of inflammatory markers. Notably, melatonin supplementation in ob/ob mice reverted these obesogenic heart alterations. Melatonin prevented heart remodeling caused by obesity through SIRT1 activation, which, together with mitochondrial pathways, reduced oxidative stress and inflammation.

Persistent organic pollutants (POPs) increase rage signaling to promote downstream cardiovascular remodeling

Exposure to environmental contaminants and consumption of a high, saturated fatty diet has been demonstrated to promote precursors for metabolic syndrome (hyperglycemia, hyperinsulinemia, and hypertriglyceridemia). The purpose of this study was to determine if exposure to the most prevalent environmental persistent organic pollutants (POPs) would act as causative agents to promote metabolic syndrome independent of dietary intake. We hypothesized that POPs will activate the advanced glycated end-product (AGE)-and receptor for AGE (RAGE) signaling cascade to promote downstream signaling modulators of cardiovascular remodeling and oxidative stress in the heart. At 5-weeks of age nondiabetic (WT) and diabetic (ob/ob) mice were exposed POPs mixtures by oral gavage twice a week for 6-weeks. At the end of 6-weeks, animals were sacrificed and the hearts were taken for biochemical analysis. Increased activation of the AGE-RAGE signaling cascade via POPs exposure resulted in elevated levels of fibroblast differentiation (α-smooth muscle actin) and RAGE expression indicated maladaptive cardiac remodeling. Conversely, the observed decreased superoxide dismutase-1 and -2 (SOD-1 and SOD-2) expression may exacerbate the adverse changes occurring as a result of POPs treatment to reduce innate cardioprotective mechanisms. In comparison, ventricular collagen levels were decreased in mice exposed to POPs. In conclusion, exposure to organic environmental pollutants may intensify oxidative and inflammatory stressors to overwhelm protective mechanisms allowing for adverse cardiac remodeling.

Cardiovascular Pleiotropic Effects of Natriuretic Peptides

Atrial natriuretic peptide (ANP) is a cardiac hormone belonging to the family of natriuretic peptides (NPs). ANP exerts diuretic, natriuretic, and vasodilatory effects that contribute to maintain water-salt balance and regulate blood pressure. Besides these systemic properties, ANP displays important pleiotropic effects in the heart and in the vascular system that are independent of blood pressure regulation. These functions occur through autocrine and paracrine mechanisms. Previous works examining the cardiac phenotype of loss-of-function mouse models of ANP signaling showed that both mice with gene deletion of ANP or its receptor natriuretic peptide receptor A (NPR-A) developed cardiac hypertrophy and dysfunction in response to pressure overload and chronic ischemic remodeling. Conversely, ANP administration has been shown to improve cardiac function in response to remodeling and reduces ischemia-reperfusion (I/R) injury. ANP also acts as a pro-angiogenetic, anti-inflammatory, and anti-atherosclerotic factor in the vascular system. Pleiotropic effects regarding brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) were also reported. In this review, we discuss the current evidence underlying the pleiotropic effects of NPs, underlying their importance in cardiovascular homeostasis.

Heart Failure With Preserved Ejection Fraction and Adipose Tissue: A Story of Two Tales

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of heart failure in the presence of a normal left ventricular ejection fraction. Although it accounts for up to 50% of all clinical presentations of heart failure, there are no evidence-based therapies for HFpEF to reduce morbidity and mortality. Additionally there is a lack of mechanistic understanding about the pathogenesis of HFpEF. HFpEF is associated with many comorbidities (such as obesity, hypertension, type 2 diabetes, atrial fibrillation, etc.) and is coupled with both cardiac and extra-cardiac abnormalities. Large outcome trials and registries reveal that being obese is a major risk factor for HFpEF. There is increasing focus on investigating the link between obesity and HFpEF, and the role that the adipose tissue and the heart, and the circulating milieu play in development and pathogenesis of HFpEF. This review discusses features of the obese-HFpEF phenotype and highlights proposed mechanisms implicated in the inter-tissue communication between adipose tissue and the heart in obesity-associated HFpEF.

Anti-inflammatory and angiogenic effects of exercise training in cardiac muscle of diabetic mice

Background: Improved glycemic control and cardiovascular function are major benefits of regular exercise training (ET) in type 2 diabetes. Recent work has demonstrated that ET improves cardiac and vascular functions independent of obesity, inflammation, and glucose control in the diabetic db/db mouse. In this study, we determined whether ET can overcome the effects of elevated inflammatory cytokines and hyperglycemia on markers of cardiac angiogenesis and inflammation in the diabetic mouse. Methods: Male diabetic db/db mice were assigned to a sedentary and exercise-trained group. Sedentary lean control littermates were used as controls. ET was performed at moderate intensity on a treadmill 5 days a week for a period of 8 weeks. After ET, blood was collected for assay of glucose, hemoglobin (HB and HB_1AC), C-reactive protein (CRP), and IL-6. Markers of inflammation and insulin resistance (IL-6, IL-1β, and tumor necrosis factor-alpha [TNF-α]) and angiogenesis (endothelial nitric oxide synthase [eNOS], vascular endothelial growth factor-A [VEGF-A], and hypoxia-inducible factor-1α [HIF-1α]) were measured in hearts. Results: Diabetic db/db mice remained obese and hyperglycemic after ET. Percent total HB and HB_1AC were significantly higher in ET db/db mice compared to sedentary db/db mice, indicating further deterioration of glucose control with ET. Plasma levels of CRP and IL-6 were higher in sedentary db/db mice compared to control mice and were unaffected by ET. However, in the presence of hyperglycemia and elevated plasma cytokines, protein expression of eNOS, mRNA expression of VEGF-A, and HIF-1α was increased in db/db hearts after ET. On the other hand, protein expression of TNF-α and mRNA expression IL-6 and IL-1β was significantly decreased by ET in hearts of db/db mice. Conclusion: Our results indicate that ET improves cardiac markers of angiogenesis, insulin resistance, and endothelial dysfunction in the db/db mouse. This was observed independently of obesity, hyperglycemia, and the systemic inflammatory state.

Regulatory Role of Endothelial PHD2 in the Hepatic Steatosis

Background/Aims:

Liver disease is a leading cause of high mortality and morbidity worldwide. The aim of the present study is to investigate the regulatory role of prolyl hydroxylase-2 (PHD2)-hypoxia-inducible factor-2α (HIF-2α) axis on nonalcoholic fatty liver disease (NAFLD) and to explore the potential mechanisms by which endothelial (EC)-specific PHD2 deficiency regulates hepatic steatosis and fibrosis.

Methods:

In the endothelial-specific PHD2 knockout (PHD2^ECKO) mouse fed with normal diet or high fat diet (HFD), liver lipid accumulation and fibrosis were measured by Oil Red O and Masson trichrome staining. The fat and body weight (FW/BW) ratio and glucose tolerance were measured. The expression of HIF-2α, atrial natriuretic peptide (ANP), angiopoietin-2 (Ang-2), and transforming growth factor-β (TGF-β) were analyzed by western blot analysis.

Results:

The steatosis and fibrosis were significantly increased in the PHD2^ECKO mice. FW/BW ratio was significantly increased in the PHD2^ECKO mice. Moreover, knockout of endothelial PHD2 resulted in an impairment of glucose tolerance in mice. Western blot analysis showed that the expression of HIF-2α in liver tissues was not significantly increased. Interestingly, the expression of ANP was decreased, and Ang-2 and TGF-β levels were significantly increased in the liver of PHD2^ECKO mice. The FW/BW ratio was also significantly increased in the PHD2^ECKO mice fed with HFD for 16 weeks. Feeding HFD resulted in a significant increase in hepatic steatosis in the control PHD2^f/f mice, but did not further enhance hepatic steatosis in the PHD2^ECKO mice.

Conclusions:

We concluded that the endothelial PHD2 plays a critical role in hepatic steatosis and fibrosis, which may be involved in the regulation of ANP and Ang-2/TGF-β signaling pathway, but not the HIF-2α expression.

Associations of Body Mass Index With Laboratory and Biomarkers in Patients With Acute Heart Failure

BACKGROUND

Plasma concentrations of natriuretic peptides decline with obesity in patients with heart failure. Whether this is true for other biomarkers is unknown. We investigated a wide range of biomarker profiles in acute heart failure across the body mass index (BMI) spectrum.

METHODS AND RESULTS

A total of 48 biomarkers, assessing multiple pathophysiological pathways, were measured in 2033 patients included in PROTECT (Placebo-Controlled Randomized Study of the Selective A1 Adenosine Receptor Antagonist Rolofylline for Patients Hospitalized With Acute Decompensated Heart Failure and Volume Overload to Assess Treatment Effect on Congestion and Renal Function), a trial comparing the effects of rolofylline to placebo in patients with acute heart failure. Patients were classified into 4 groups according to BMI (<25, 25-30, 30-35, and >35 kg/m²). Of 2003 patients with known weight and height, mean age was 70±12 years and 67% were men. Patients with a higher BMI (>35 kg/m²) had higher blood pressures, were younger, and were more often women. Median levels of brain natriuretic peptide were 550 pg/mL in patients with a BMI <25 kg/m² and 319 pg/mL in patients with a BMI >35 kg/m² (P<0.001). Multivariable regression revealed that brain natriuretic peptide (β=-0.250; P<0.001) and receptor for advanced glycation endproducts (β=-0.095; P<0.007) were inversely correlated to BMI, whereas higher levels of uric acid (β=0.164; P<0.001), proadrenomedullin (β=0.171; P<0.001), creatinine (β=0.118; P=0.003), sodium (β=0.101; P=0.006), and bicarbonate (β=0.094; P=0.009) were associated with higher BMI. No significant interaction was seen between these 7 biomarkers and BMI on 180-day mortality.

CONCLUSIONS

The plasma concentrations of several biomarkers are either positively or negatively influenced by BMI. These findings suggest that these markers should be interpreted with caution in patients with obesity. Although concentrations differ, their prognostic value for mortality up to 180 days did not differ.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00354458.

The effects of exercise training and caloric restriction on the cardiac oxytocin natriuretic peptide system in the diabetic mouse

BACKGROUND

Regular exercise training (ET) and caloric restriction (CR) are the frontline strategies in the treatment of type 2 diabetes mellitus with the aim at reducing cardiometabolic risk. ET and CR improve body weight and glycemic control, and experimental studies indicate that these paradigms afford cardioprotection. In this study, the effects of combined ET and CR on the cardioprotective oxytocin (OT)-natriuretic peptide (NP) system were determined in the db/db mouse, a model of type 2 diabetes associated with insulin resistance, hyperglycemia, and obesity.

METHODS

Five-week-old male db/db mice were assigned to the following groups: sedentary, ET, and ET + CR. Nonobese heterozygote littermates served as controls. ET was performed on a treadmill at moderate intensity, and CR was induced by reducing food intake by 30% of that consumed by sedentary db/db mice for a period of 8 weeks.

RESULTS

After 8 weeks, only ET + CR, but not ET, slightly improved body weight compared to sedentary db/db mice. Regardless of the treatment, db/db mice remained hyperglycemic. Hearts from db/db mice demonstrated reduced expression of genes linked to the cardiac OT-NP system. In fact, compared to control mice, mRNA expression of GATA binding protein 4 (GATA4), OT receptor, OT, brain NP, NP receptor type C, and endothelial nitric oxide synthase (eNOS) was decreased in hearts from sedentary db/db mice. Both ET alone and ET + CR increased the mRNA expression of GATA4 compared to sedentary db/db mice. Only ET combined with CR produced increased eNOS mRNA and protein expression.

CONCLUSION

Our data indicate that enhancement of eNOS by combined ET and CR may improve coronary endothelial vasodilator dysfunction in type 2 diabetes but did not prevent the downregulation of cardiac expression in the OT-NP system, possibly resulting from the sustained hyperglycemia and obesity in diabetic mice.

A low-carbohydrate high-fat diet decreases lean mass and impairs cardiac function in pair-fed female C57BL/6J mice

Background

Excess body fat is a major health issue and a risk factor for the development of numerous chronic diseases. Low-carbohydrate diets like the Atkins Diet are popular for rapid weight loss, but the long-term consequences remain the subject of debate. The Scandinavian low-carbohydrate high-fat (LCHF) diet, which has been popular in Scandinavian countries for about a decade, has very low carbohydrate content (~5 E %) but is rich in fat and includes a high proportion of saturated fatty acids. Here we investigated the metabolic and physiological consequences of a diet with a macronutrient composition similar to the Scandinavian LCHF diet and its effects on the organs, tissues, and metabolism of weight stable mice.

Methods

Female C57BL/6J mice were iso-energetically pair-fed for 4 weeks with standard chow or a LCHF diet. We measured body composition using echo MRI and the aerobic capacity before and after 2 and 4 weeks on diet. Cardiac function was assessed by echocardiography before and after 4 weeks on diet. The metabolic rate was measured by indirect calorimetry the fourth week of the diet. Mice were sacrificed after 4 weeks and the organ weight, triglyceride levels, and blood chemistry were analyzed, and the expression of key ketogenic, metabolic, hormonal, and inflammation genes were measured in the heart, liver, and adipose tissue depots of the mice using real-time PCR.

Results

The increase in body weight of mice fed a LCHF diet was similar to that in controls. However, while control mice maintained their body composition throughout the study, LCHF mice gained fat mass at the expense of lean mass after 2 weeks. The LCHF diet increased cardiac triglyceride content, impaired cardiac function, and reduced aerobic capacity. It also induced pronounced alterations in gene expression and substrate metabolism, indicating a unique metabolic state.

Conclusions

Pair-fed mice eating LCHF increased their percentage of body fat at the expense of lean mass already after 2 weeks, and after 4 weeks the function of the heart deteriorated. These findings highlight the urgent need to investigate the effects of a LCHF diet on health parameters in humans.

Roux-en-Y gastric bypass alleviates hypertension and is associated with an increase in mid-regional pro-atrial natriuretic peptide in morbid obese patients

OBJECTIVE

To examine 24-h blood pressure (24BP), systemic haemodynamics and the effect of sodium intake on 24BP in obese patients before and after gastric bypass surgery [laparoscopic Roux-en-Y gastric bypass (LRYGB)], and to determine whether weight loss from LRYGB might be related to an increase in plasma concentrations of atrial natriuretic peptide.

METHODS

Twelve hypertensive and 12 normotensive morbidly obese patients underwent LRYGB: 24BP, systemic haemodynamics and mid-regional pro-atrial natriuretic peptide (MRproANP) were assessed before, 6 weeks and 12 months after surgery. The effect of high versus low sodium intake on 24BP was evaluated before and 12 months after LRYGB.

RESULTS

Six weeks after LRYGB, the average weight loss was 20 kg, with a further 21 kg weight loss 1 year after surgery. In hypertensive patients, 24BP was significantly reduced at 6 weeks, but not 1 year after LRYGB. However, antihypertensive medications were successively reduced from baseline to 1 year after surgery. In normotensive patients, there was no change in 24BP 6 weeks after LRYGB, but a tendency towards a reduction 1 year after the operation. Plasma concentrations of MRproANP were subnormal prior to surgery in hypertensive patients and increased by 77% 1 year after the operation. In normotensive patients, preoperative concentrations were normal and increased only by 6%. High sodium intake induced plasma volume expansion, increased stroke volume and cardiac output, but no significant change in 24BP - neither before nor after LRYGB.

CONCLUSIONS

LRYGB resulted in a significant 24BP reduction and a substantial increase in MRproANP plasma concentrations in hypertensive, obese patients 6 weeks after surgery, suggesting a causal link between obesity-hypertension and altered release/degradation of cardiac natriuretic peptides.

Regulation of B-type natriuretic peptide synthesis by insulin in obesity in male mice

Human studies suggest that insulin resistance and obesity are associated with a decrease in B-type natriuretic peptide (BNP) plasma concentrations. The objective of the study was to gain insights into the mechanisms involved in the association between insulin resistance and decreased BNP plasma concentrations. Mice fed a high-fat, high-fructose (HFHF) diet for 4 weeks developed mild obesity and systemic insulin resistance. Elevated plasma concentrations of insulin, glucose and triglycerides were noted. The HFHF diet was also associated with myocardial insulin resistance, characterized by an impaired response of the phosphoinositide 3-kinase-AKT (PI3K-AKT) pathway to insulin in the left ventricle. Myocardial BNP expression and protein were decreased in HFHF-fed mice compared with control animals. Exposure of cardiomyocytes to 100 nm insulin activated PI3K-AKT signalling (15 min) and induced a 1.9 ± 0.3-fold increase in BNP gene expression (6 h). Prolonged exposure of cardiomyocytes to a high insulin concentration (100 nm) for 48 h induced insulin resistance, characterized by an impaired response of the PI3K-AKT signalling pathway and a decreased response of the BNP gene expression to insulin. The decreased response in BNP gene expression was reproduced by treating cardiomyocytes for 7 h with a PI3-kinase inhibitor (wortmannin). In conclusion, HFHF diet in vivo, prolonged exposure to an elevated concentration of insulin or inhibition of the PI3K-AKT pathway in vitro all decrease BNP mRNA levels; this decrease may in turn contribute to the decreased BNP peptide concentrations in plasma observed in insulin-resistant individuals.

Increased serum soluble corin in dyslipidemia: A cross-sectional study

BACKGROUND

Natriuretic peptides have been associated with dyslipidemia. As a physiological activator of natriuretic peptides, corin might also be associated with dyslipidemia. However, this association has not yet been studied in Chinese populations.

METHODS

Serum soluble corin and blood lipid profiles were determined for 2496 participants aged above 30y. A logistic regression model was applied to evaluate the association between serum soluble corin and dyslipidemia.

RESULTS

Serum soluble corin was significantly increased in participants with dyslipidemia in both men (P<0.001) and women (P<0.001). After controlling for the confounding factors, OR of dyslipidemia positively increased with increasing levels of serum soluble corin in men (P for trend=0.011) and women (P for trend=0.043). Participants with a high corin level were more likely to have dyslipidemia than those with a low corin level in men (OR, 95% CI: 1.45, 1.07-1.97) and women (OR, 95% CI: 1.33, 1.04-1.70).

CONCLUSION

Serum soluble corin was significantly and positively associated with dyslipidemia. Our findings suggested that serum soluble corin may be a marker or risk factor for dyslipidemia.

Cardiac natriuretic peptides in plasma increase after dietary induced weight loss in obesity

Background

Cardiac natriuretic peptides are established biomarkers in heart disease, but are also affected by body mass index (BMI). The purpose of the present study was to examine the impact of weight loss and changes in body composition following dietary intervention on plasma concentrations of the prohormones to A- and B-type natriuretic peptides (proANP and proBNP) and adrenomedullin (proADM).

Results

A total of 52 healthy obese subjects, 47 women and 5 men (BMI 36.5 ± 5.6 kg/m²) were randomised to either an intensive weight reduction programme using a combination of very low calorie diet (810 kcal/day) and conventional hypo-energetic diet (1200 kcal/day) for 52 weeks, or to a control group that was offered diet-related counselling. N-terminal proBNP (NT-proBNP), mid-regional proANP (MR-proANP) and proADM (MR-proADM) and body composition using dual-energy x-ray absorptiometry (DEXA) scanning were determined at baseline and after 52 weeks. Comparisons between groups were analysed using t-tests. Changes from the baseline within the groups were analysed with paired tests. Changes in the variables, delta (∆), were calculated as 52 weeks minus the baseline.

In the intervention group, BMI decreased by almost 20% (31.6 ± 6.2 vs. 37.1 ± 6.1 kg/m²; P <0.001) with a loss of body fat of 23.5 ± 15.5% (P < 0.001). Plasma concentrations of NT-proBNP and MR-proANP increased (from 55 ± 31 to 97 ± 55 pg/ml; P < 0.001, and from 59 ± 21 to 74 ± 26 pmol/L; P < 0.001), whereas MR-proADM decreased (from 573 ± 153 to 534 ± 173 pmol/L; P <0.001). Changes (Δ) in MR-proANP correlated with Δfat mass (r = −0.359; P = 0.011) and Δglucose (r = −0.495; P <0.001), while increases in NT-proBNP were primarily associated with reduced plasma glucose (r = −0.462; P <0.001). A modest but significant weight loss of 6% (P < 0.001) was found in the control group with no changes in plasma concentrations of NT-proBNP or MR-proANP, and a minor change in MR-proADM.

Conclusions

Plasma NT-proBNP and MR-proANP concentrations increase and MR-proADM concentration decreases during weight loss, underlining the dynamic impact of BMI, body composition and glucose metabolism on these cardiovascular biomarkers.

Natriuretic peptides, heart, and adipose tissue: new findings and future developments for diabetes research

Natriuretic peptides (NPs) play a key role in cardiovascular homeostasis, counteracting the deleterious effects of volume and pressure overload and activating antibrotic and antihypertrophic pathways in the heart. N-terminal B-type NP (NT-proBNP) also is a promising biomarker of global cardiovascular risk in the general population, and there is increasing interest on its potential use in diabetic patients for screening of silent cardiovascular abnormalities, cardiovascular risk stratification, and guided intervention. Recently, both atrial NP (ANP) and B-type NP (BNP) have emerged as key mediators in the control of metabolic processes including the heart in the network of organs that regulate energy usage and metabolism. Epidemiological studies have shown that ANP and BNP are reduced in people with obesity, insulin resistance, and diabetes, and this deficiency may contribute to enhance their global cardiovascular risk. Moreover, ANP and BNP have receptors in the adipose tissue, enhance lipolysis and energy expenditure, and modulate adipokine release and food intake. Therefore, low ANP and BNP levels may be not only a consequence but also a cause of obesity, and recent prospective studies have shown that low levels of NT-proBNP and midregional proANP (MR-proANP) are a strong predictor of type 2 diabetes onset. Whether ANP and BNP supplementation may result in either cardiovascular or metabolic benefits in humans remains, however, to be established.

Sinoatrial node dysfunction induces cardiac arrhythmias in diabetic mice

BACKGROUND

The aim of this study was to probe cardiac complications, including heart-rate control, in a mouse model of type-2 diabetes. Heart-rate development in diabetic patients is not straight forward: In general, patients with diabetes have faster heart rates compared to non-diabetic individuals, yet diabetic patients are frequently found among patients treated for slow heart rates. Hence, we hypothesized that sinoatrial node (SAN) dysfunction could contribute to our understanding of the mechanism behind this conundrum and the consequences thereof.

METHODS

Cardiac hemodynamic and electrophysiological characteristics were investigated in diabetic db/db and control db/+ mice.

RESULTS

We found improved contractile function and impaired filling dynamics of the heart in db/db mice, relative to db/+ controls. Electrophysiologically, we observed comparable heart rates in the two mouse groups, but SAN recovery time was prolonged in diabetic mice. Adrenoreceptor stimulation increased heart rate in all mice and elicited cardiac arrhythmias in db/db mice only. The arrhythmias emanated from the SAN and were characterized by large RR fluctuations. Moreover, nerve density was reduced in the SAN region.

CONCLUSIONS

Enhanced systolic function and reduced diastolic function indicates early ventricular remodeling in obese and diabetic mice. They have SAN dysfunction, and adrenoreceptor stimulation triggers cardiac arrhythmia originating in the SAN. Thus, dysfunction of the intrinsic cardiac pacemaker and remodeling of the autonomic nervous system may conspire to increase cardiac mortality in diabetic patients.

Treatment with brain natriuretic peptide prevents the development of cardiac dysfunction in obese diabetic db/db mice

AIMS/HYPOTHESIS

Obesity and diabetes increase the risk of developing cardiovascular diseases and heart failure. These metabolic disorders are generally reflected by natriuretic peptide system deficiency. Since brain natriuretic peptide (BNP) is known to influence metabolism and cardioprotection, we investigated the effect of chronic exogenous BNP treatment on adverse myocardial consequences related to obesity and diabetes.

METHODS

Ten-week-old C57BL/KsJ-db/db obese diabetic mice (db/db) and their lean control littermates (db/+) were treated with BNP (0.6 μg kg(-1) h(-1)) or saline for 12 weeks (n = 10/group). Serial blood and tomography analysis were performed. Cardiac function was determined by echocardiography, and biochemical and histological heart and fat analyses were also performed.

RESULTS

BNP treatment resulted in an average increase in plasma BNP levels of 70 pg/ml. An improvement in the metabolic profile of db/db mice was observed, including a reduction in fat content, increased insulin sensitivity, improved glucose tolerance and lower blood glucose, despite increased food intake. db/db mice receiving saline displayed both early systolic and diastolic dysfunction, whereas these functional changes were prevented by BNP treatment. The cardioprotective effects of BNP were attributed to the inhibition of cardiomyocyte apoptosis, myocardial fibrosis, cardiac hypertrophy and the AGE-receptor for AGE (RAGE) system as well as normalisation of cardiac AMP-activated protein kinase and endothelial nitric oxide synthase activities.

CONCLUSIONS/INTERPRETATION

Our results indicate that chronic BNP treatment at low dose improves the metabolic profile and prevents the development of myocardial dysfunction in db/db mice.

Natriuretic peptides in cardiometabolic regulation and disease

In the 30 years since the identification of the natriuretic peptides, their involvement in regulating fluid and blood pressure has become firmly established. Data indicating a role for these hormones in lifestyle-related metabolic and cardiovascular disorders have also accumulated over the past decade. Dysregulation of the natriuretic peptide system has been associated with obesity, glucose intolerance, type 2 diabetes mellitus, and essential hypertension. Moreover, the natriuretic peptides have been implicated in the protection against atherosclerosis, thrombosis, and myocardial ischaemia. All these conditions can coexist and potentially lead to heart failure, a syndrome associated with a functional natriuretic peptide deficiency despite high circulating concentrations of immunoreactive peptides. Therefore, dysregulation of the natriuretic peptide system, a 'natriuretic handicap', might be an important factor in the initiation and progression of metabolic dysfunction and its accompanying cardiovascular complications. This Review provides a summary of the natriuretic peptide system and its involvement in these cardiometabolic conditions. We propose that these peptides might have an integrating role in lifestyle-related metabolic and cardiovascular disorders.

All-trans retinoic acid stimulates gene expression of the cardioprotective natriuretic peptide system and prevents fibrosis and apoptosis in cardiomyocytes of obese ob/ob mice

In hypertensive rodents, retinoic acid (RA) prevents adverse cardiac remodelling and improves myocardial infarction outcome, but its role in obesity-related changes of cardiac tissue are unclear. We hypothesized that all-trans RA (ATRA) treatment will improve the cardioprotective oxytocin-natriuretic peptides (OT-NP) system, preventing apoptosis and collagen accumulation in hearts of ob/ob mice, a mouse model of obesity and insulin resistance. Female 9-week-old B6.V-Lep/J ob/ob mice (n = 16) were divided into 2 groups: 1 group (n = 8) treated with 100 μg of ATRA dissolved in 100 μL of corn oil (vehicle) delivered daily (∼2 μg·g body weight(-1)·day(-1)) by stomach intubation for 16 days, and 1 group (n = 8) that received the vehicle alone. A group of nonobese littermate mice (n = 9) served as controls. Ob/ob mice exhibited obesity, hyperglycaemia, and downregulation of the cardiac OT-NP system, including the mRNA for the transcription factor GATA4, OT receptor and brain NP, and the protein expression for endothelial nitric oxide synthase. Hearts from ob/ob mice also demonstrated increased apoptosis and collagen accumulation. ATRA treatment induced weight loss and decreased adipocytes diameter in the visceral fat, thus reducing visceral obesity, which is associated with a high risk for cardiovascular disease. RA treatment was associated with a reduction in hyperglycemia and a normalization of the OT-NP system's expression in the hearts of ob/ob mice. Furthermore, ATRA treatment prevented apoptosis and collagen accumulation in hearts of ob/ob mice. The present study indicates that ATRA treatment was effective in restoring the cardioprotective OT-NP system and in preventing abnormal cardiac remodelling in the ob/ob mice.

The associations between metabolic variables and NT-proBNP are blunted at pathological ranges: the Multi-Ethnic Study of Atherosclerosis

OBJECTIVE

Under physiological conditions brain natriuretic peptide (BNP) is inversely associated with metabolic risk factors, but under pathological conditions these associations may tend to plateau.

MATERIAL AND METHODS

5597 individuals in the Multi-Ethnic Study of Atherosclerosis (MESA), 45-84years of age, free of overt cardiovascular disease in 2000-02 and then again in 2003-05 participated in this study. Associations between NT-proBNP and BMI, blood lipids, homeostasis model of insulin resistance (HOMA-IR) using linear regression models were adjusted for age, race, sex, BMI, % of energy from saturated fats, intentional exercise, statin use, antihypertensive medication use, diabetes and glomerular filtration rate. The inflection points (IP) at which these associations became nonlinear were determined using linear splines with knots at different levels of NT-proBNP.

RESULTS

Participants with NT-proBNP ≥100pg/mL (29%) tended to be older, on statins and anti-hypertensive medications vs. those with NT-proBNP <100pg/mL. The IP point varies among variables and ranged from 50-120pg/mL. NT-proBNP<IP, associated inversely with BMI, total cholesterol (TC), LDL-C, triglycerides (TG) and HOMA-IR, but positively with HDL-C. A higher proportion of participants with NT-proBNP ≥100pg/mL had subclinical CVD. All associations with NT-proBNP plateaued when NT-proBNP≥IP. Baseline level in NT-proBNP was not associated with 3-year change in BMI, TG, HDL-C or fasting glucose.

CONCLUSIONS

In a large cardiovascular disease-free cohort, NT-proBNP within the lower (physiological) range was inversely associated with TC, LDL-C, TG and insulin resistance with different inflection points, but at higher (pathological) levels these associations were blunted.

Metabolic rather than body composition measurements are associated with lower serum natriuretic peptide concentrations in normal weight and obese men

BACKGROUND

Several studies have shown that obese persons have lower circulating natriuretic peptide (NP) concentrations. The cause of the relative NP deficiency seen in obese persons is poorly understood, although variation in body composition and metabolic abnormalities has been suggested to play a role. Thus, the aim of this study was to assess whether variation in circulating NP concentrations would be associated with differences in metabolic disturbances rather than with differences in body composition.

METHODS

In 27 normal weight men (body mass index (BMI) = 20.0-24.9kg/m(2)) and 103 obese men (BMI ≥ 30kg/m(2)), we determined body composition (total, android, and gynoid fat mass) by dual energy x-ray absorptiometry scanning, and we measured fasting serum concentrations of midregional proatrial NP (MR-proANP) and insulin, as well as fasting plasma glucose concentrations.

RESULTS

Mean weight ± SD was 74.9±6.7kg in the normal weight men and 106.1±10.8kg in obese men. Applying multiple regressions, adjusting for age and weight status (normal weight vs. obese), serum MR-proANP concentrations were significantly inversely associated with serum insulin concentrations (β = -0.39; P < 0.0001) and plasma glucose concentrations (β = -0.21; P = 0.02) but not with total (β = 0.00), android (β = -0.01), or gynoid (β = 0.03) fat mass percentage (P > 0.76). No significant interaction effects between metabolic measurements or body composition measurements and weight status on MR-proANP concentrations were found (P > 0.08).

CONCLUSIONS

In normal weight and obese men, lower circulating NP concentrations are associated with higher insulin and glucose concentrations and not with the proportion of total fat mass or the distribution of fat mass.

A systematic review of fetal genes as biomarkers of cardiac hypertrophy in rodent models of diabetes

Pathological cardiac hypertrophy activates a suite of genes called the fetal gene program (FGP). Pathological hypertrophy occurs in diabetic cardiomyopathy (DCM); therefore, the FGP is widely used as a biomarker of DCM in animal studies. However, it is unknown whether the FGP is a consistent marker of hypertrophy in rodent models of diabetes. Therefore, we analyzed this relationship in 94 systematically selected studies. Results showed that diabetes induced with cytotoxic glucose analogs such as streptozotocin was associated with decreased cardiac weight, but genetic or diet-induced models of diabetes were significantly more likely to show cardiac hypertrophy (P<0.05). Animal strain, sex, age, and duration of diabetes did not moderate this effect. There were no correlations between the heart weight:body weight index and mRNA or protein levels of the fetal genes α-myosin heavy chain (α-MHC) or β-MHC, sarco/endoplasmic reticulum Ca²⁺-ATPase, atrial natriuretic peptide (ANP), or brain natriuretic peptide. The only correlates of non-indexed heart weight were the protein levels of α-MHC (Spearman's ρ = 1, P<0.05) and ANP (ρ = −0.73, P<0.05). These results indicate that most commonly measured genes in the FGP are confounded by diabetogenic methods, and are not associated with cardiac hypertrophy in rodent models of diabetes.

Unexpected effects of voluntary exercise training on natriuretic peptide and receptor mRNA expression in the ob/ob mouse heart

Regular exercise is generally recommended for the treatment of obesity and type 2 diabetes. Exercise reduces body weight, improves glycemic control and cardiovascular (CV) function. This study was designed to determine the impact of voluntary wheel running on the cardiac oxytocin (OT)-natriuretic peptide (NP) system and plasma CV risk factors in the ob/ob mouse, a model of insulin resistance coupled with severe obesity. Five-week-old male ob/ob mice and non-obese heterozygote control littermates were assigned to either a sedentary or running group. Voluntary running was performed using a wheel system for a period of 8 weeks. Compared to non-obese mice, daily running activity expressed in kilometers, was significantly lower in ob/ob mice. In these mice, voluntary running improved body weight, but exacerbated CV markers, including plasma glucose and triglyceride levels. OT receptor gene expression was decreased in hearts of ob/ob mice compared to non-obese mice, and no improvement in the expression of this receptor was observed after voluntary running. Hearts from ob/ob mice also expressed lower BNP mRNA, whereas no differences in A- and C-type NP were observed between non-obese and ob/ob mice. After voluntary running, a downregulation in the expression of all three NPs coupled with increased apoptosis was observed in ob/ob hearts. Our results show that voluntary exercise running activity was decreased in the ob/ob mouse. Surprisingly, this was associated with a worsening of common CV plasma markers, reduced expression of peptides linked to the cardioprotective OT-NP system, and increased expression of cardiac apoptotic markers.

Body mass index in chronic heart failure: association with biomarkers of neurohormonal activation, inflammation and endothelial dysfunction

BACKGROUND

Low body mass index (BMI) is associated with a poor outcome in chronic heart failure (CHF). An inverse association between BMI and adiponectin and N-terminal pro-B-type natriuretic peptide (NT-proBNP) has been reported. The aim of the present study was to investigate whether novel markers of neurohormonal activation, inflammation, and endothelial dysfunction are associated with BMI in CHF.

METHODS

In a cross-sectional study including 171 patients with CHF and a left ventricular ejection fraction (LVEF) ≤45% the impact of BMI on circulating plasma concentrations of adiponectin, α-defensins, high sensitivity C-reactive protein (hsCRP), copeptin, mid-regional pro-adrenomedullin (MR-proADM), NT-proBNP, and mid-regional pro-A-type natriuretic peptide (MR-proANP) were evaluated.

RESULTS

In multivariable linear regression analysis including age, sex, LVEF, New York Heart Association functional classification (NYHA), estimated glomerular filtration rate (eGFR), and diabetes, only NT-proBNP (β = -0.32) and adiponectin (β = -0.39) remained independently associated with BMI. MR-proANP was associated with BMI but adjusting for age attenuated the relation being no longer significant.

CONCLUSIONS

Among biomarkers typically increased in patients with CHF only adiponectin and NT-proBNP demonstrated independent inverse associations with BMI. This indicates a direct effect of these two biomarkers enhancing the wasting process seen in CHF.

The endocrinology of food intake

Many questions must be considered with regard to consuming food, including when to eat, what to eat and how much to eat. Although eating is often thought to be a homeostatic behaviour, little evidence exists to suggest that eating is an automatic response to an acute shortage of energy. Instead, food intake can be considered as an integrated response over a prolonged period of time that maintains the levels of energy stored in adipocytes. When we eat is generally determined by habit, convenience or opportunity rather than need, and meals are preceded by a neurally-controlled coordinated secretion of numerous hormones that prime the digestive system for the anticipated caloric load. How much we eat is determined by satiation hormones that are secreted in response to ingested nutrients, and these signals are in turn modified by adiposity hormones that indicate the fat content of the body. In addition, many nonhomeostatic factors, including stress, learning, palatability and social influences, interact with other controllers of food intake. If a choice of food is available, what we eat is based on pleasure and past experience. This article reviews the hormones that mediate and influence these processes.

Docosahexaenoic acid supplementation does not improve Western diet-induced cardiomyopathy in rats

Obesity increases risk for cardiomyopathy in the absence of hypertension, diabetes or ischemia. The fatty acid milieu, modulated by diet, may modify myocardial structure and function, lending partial explanation for the array of cardiomyopathic phenotypy. We sought to identify gross, cellular and ultrastructural myocardial changes associated with Western diet intake, and subsequent modification with docosahexaenoic acid (DHA) supplementation. Wistar and Sprague-Dawley (SD) rats received 1 of 3 diets: control (CON); Western (WES); Western + DHA (WES+DHA). After 12 weeks of treatment, echocardiography was performed and myocardial adiponectin, fatty acids, collagen, area occupied by lipid and myocytes, and ultrastructure were determined. Strain effects included higher serum adiponectin in Wistar rats, and differences in myocardial fatty acid composition. Diet effects were evident in that both WES and WES+DHA feeding were associated with similarly increased left ventricular (LV) diastolic cranial wall thickness (LVW(cr/d)) and decreased diastolic internal diameter (LVID(d)), compared to CON. Unexpectedly, WES+DHA feeding was associated additionally with increased thickness of the LV cranial wall during systole (LVW(cr/s)) and the caudal wall during diastole (LVW(ca/d)) compared to CON; this was observed concomitantly with increased serum and myocardial adiponectin. Diastolic dysfunction was present in WES+DHA rats compared to both WES and CON. Myocyte cross sectional area (CSA) was greater in WES compared to CON rats. In both fat-fed groups, transmission electron microscopy (TEM) revealed myofibril degeneration, disorganized mitochondrial cristae, lipid inclusions and vacuolation. In the absence of hypertension and whole body insulin resistance, WES+DHA intake was associated with more global LV thickening and with diastolic dysfunction, compared to WES feeding alone. Myocyte hypertrophy, possibly related to subcellular injury, is an early change that may contribute to gross hypertrophy. Strain differences in adipokines and myocardial fatty acid accretion may underlie heterogeneous data from rodent studies.

Natriuretic peptides and cGMP signaling control of energy homeostasis

Since the discovery of natriuretic peptides (NPs) by de Bold et al. in 1981, the cardiovascular community has been well aware that they exert potent effects on vessels, heart remodeling, kidney function, and the regulation of sodium and water balance. Who would have thought that NPs are also able to exert metabolic effects and contribute to an original cross talk between heart, adipose tissues, and skeletal muscle? The attention on the metabolic role of NPs was awakened in the year 2000 with the discovery that NPs exert potent lipolytic effects mediated by the NP receptor type A/cGMP pathway in human fat cells and that they contribute to lipid mobilization in vivo. In this review, we will discuss the biological effects of NPs on the main tissues involved in the regulation of energy metabolism (i.e., white and brown adipose tissues, skeletal muscle, liver, and pancreas). These recent results on NPs are opening a new chapter into the physiological properties and therapeutic usefulness of this family of hormones.

Expression of cardiac GATA4 and downstream genes after exercise training in the db/db mouse

GATA4 is a transcriptional factor expressed in heart that regulates the synthesis of structural and cardioprotective genes. We have demonstrated that low GATA4 expression in the db/db mouse heart is associated with reduced expression of key downstream genes, including oxytocin (OT) natriuretic peptide (A-, B-type), nitric oxide synthase (eNOS), and myosin heavy chain (α-MHC). In this study, the effect of exercise on GATA4 expression and related genes was determined in the db/db mouse, a model that represents human type 2 diabetes. Vascular endothelial growth factor (VEGF) and hypoxia-induced factor-α expression were also measured after 8 weeks of treadmill running. Compared with control littermates, db/db mice exhibited hyperglycemia and obesity, and exercise failed to improve these parameters. GATA4 expression was reduced in db/db hearts and this was associated with reduced expression of OT, OTR, ANP, BNP, eNOS, α-MHC, and ratio of α- to β-MHC, whereas mRNA expression of β-MHC and VEGF remained unchanged compared with control hearts. Exercise training increased GATA4 expression (mRNA and protein) but most genes regulated by GATA4 were not observed to increase accordingly. However, protein expression of eNOS, mRNA expression of α-MHC, ratio of α- to β-MHC, and protein expression of VEGF were increased in db/db hearts after exercise. In conclusion, while GATA4 expression is increased following exercise, not all structural and cardioprotective genes are expressed, suggesting other transcription factors may be involved in this regulation. Regardless of this effect, the positive effect of exercise training on key protective genes is evident in the db/db mouse heart.

Renal, retinal and cardiac changes in type 2 diabetes are attenuated by macitentan, a dual endothelin receptor antagonist

AIMS

Diabetes is known to cause alteration of the endothelin (ET) system. We have previously demonstrated that ETs regulate augmented production of extracellular matrix proteins causing structural alterations in type 1 diabetes. Here we investigated the effects of macitentan, an orally-active, tissue-targeting dual ET receptor antagonist on chronic complications in type 2 diabetes.

MAIN METHODS

db/db mice and their age- and sex-matched controls were examined after 2 and 4 months of diabetes. Groups of diabetic animals were treated with oral macitentan (25mg/kg/day). The animals were monitored with respect to body weight and blood glucose. Urine analyses were performed for albumin. Cardiac hemodynamic studies were carried out. Renal, cardiac and retinal tissues were analyzed for ET-1, transforming growth factor-β1 (TGF-β1), vascular endothelial growth factor (VEGF), fibronectin (FN), extradomain B containing FN (EDB(+)FN) and collagen α-I (IV) mRNA. Cardiac atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were measured. Protein expressions were measured by ELISA and Western blot. Microscopic analyses were performed in the kidneys.

KEY FINDINGS

Diabetic animals showed hyperglycemia, increased urinary albumin and augmented serum creatinine levels. Diabetes caused increased renal, cardiac and retinal ET-1, TGF-β1, VEGF, FN, EDB(+)FN, collagen α-I(IV) mRNA expression along with increased FN and collagen protein and NF-κB activation. Diabetic mice also demonstrated mesangial expansion, cardiac dysfunction and increased expression of ANP and BNP. Treatment with macitentan attenuated such abnormalities.

SIGNIFICANCE

These experiments confirmed that ET system plays a significant role in the pathogenesis of chronic complications in type 2 diabetes. Such diabetes induced changes can be reduced macitentan therapy.

Obesity and risk of vascular disease: importance of endothelium-dependent vasoconstriction

Obesity has become a serious global health issue affecting both adults and children. Recent devolopments in world demographics and declining health status of the world's population indicate that the prevalence of obesity will continue to increase in the next decades. As a disease, obesity has deleterious effects on metabolic homeostasis, and affects numerous organ systems including heart, kidney and the vascular system. Thus, obesity is now regarded as an independent risk factor for atherosclerosis-related diseases such as coronary artery disease, myocardial infarction and stroke. In the arterial system, endothelial cells are both the source and target of factors contributing to atherosclerosis. Endothelial vasoactive factors regulate vascular homeostasis under physiological conditions and maintain basal vascular tone. Obesity results in an imbalance between endothelium-derived vasoactive factors favouring vasoconstriction, cell growth and inflammatory activation. Abnormal regulation of these factors due to endothelial cell dysfunction is both a consequence and a cause of vascular disease processes. Finally, because of the similarities of the vascular pathomechanisms activated, obesity can be considered to cause accelerated, 'premature' vascular aging. Here, we will review some of the pathomechanisms involved in obesity-related activation of endothelium-dependent vasoconstriction, the clinical relevance of obesity-associated vascular risk, and therapeutic interventions using 'endothelial therapy' aiming at maintaining or restoring vascular endothelial health.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Paradoxical clearance of natriuretic peptide between pulmonary and systemic circulation: a pulmonary mechanism of maintaining natriuretic peptide plasma concentration in obese individuals

CONTEXT

Although it has been reported that obese patients have low levels of natriuretic peptide, the metabolism of natriuretic peptide in this population remains unclear.

OBJECTIVES

This study aimed to examine the effects of body mass index on the natriuretic peptide clearance rate from the pulmonary and systemic circulation.

DESIGN

We conducted a prospective observational cohort study.

SETTING/PATIENTS

Thirty patients with atrial fibrillation undergoing pulmonary vein isolation in single center participated in the study.

MAIN OUTCOMES AND MEASURES

We measured pulmonary and systemic atrial/brain natriuretic peptide clearance and clinical parameters including body mass index and pulmonary oxygen levels.

RESULTS

Significantly lower atrial natriuretic peptide levels were found in all pulmonary veins when compared with the pulmonary artery. The pulmonary atrial natriuretic peptide clearance rate was negatively correlated with body mass index. In contrast, the systemic atrial natriuretic peptide clearance rate was positively correlated with the body mass index. A reciprocal relationship therefore exists between pulmonary and systemic atrial natriuretic peptide clearance. Regional pulmonary atrial natriuretic peptide clearances in the inferior lung were significantly negatively correlated to oxygen pressure in the inferior pulmonary veins. There was a similar tendency for brain natriuretic peptide, but the differences between the pulmonary artery and each pulmonary vein were not significant.

CONCLUSIONS

Overweight patients have higher systemic atrial natriuretic peptide clearance, whereas they show a lower pulmonary atrial natriuretic peptide clearance, which might be related to pulmonary tissue hypoxia.

The role of dietary fatty acids in predicting myocardial structure in fat-fed rats

Background

Obesity increases the risk for development of cardiomyopathy in the absence of hypertension, diabetes or myocardial ischemia. Not all obese individuals, however, progress to heart failure. Indeed, obesity may provide protection from cardiovascular mortality in some populations. The fatty acid milieu, modulated by diet, may modify obesity-induced myocardial structure and function, lending partial explanation for the array of cardiomyopathic phenotypy in obese individuals.

Methods

Adult male Sprague-Dawley rats were fed 1 of the following 4 diets for 32 weeks: control (CON); 50% saturated fat (SAT); 40% saturated fat + 10% linoleic acid (SAT+LA); 40% saturated fat + 10% α-linolenic acid (SAT+ALA). Serum leptin, insulin, glucose, free fatty acids and triglycerides were quantitated. In vivo cardiovascular outcomes included blood pressure, heart rate and echocardiographic measurements of structure and function. The rats were sacrificed and myocardium was processed for fatty acid analysis (TLC-GC), and evaluation of potential modifiers of myocardial structure including collagen (Masson's trichrome, hydroxyproline quantitation), lipid (Oil Red O, triglyceride quantitation) and myocyte cross sectional area.

Results

Rats fed SAT+LA and SAT+ALA diets had greater cranial LV wall thickness compared to rats fed CON and SAT diets, in the absence of hypertension or apparent insulin resistance. Treatment was not associated with changes in myocardial function. Myocardial collagen and triglycerides were similar among treatment groups; however, rats fed the high-fat diets, regardless of composition, demonstrated increased myocyte cross sectional area.

Conclusions

Under conditions of high-fat feeding, replacement of 10% saturated fat with either LA or ALA is associated with thickening of the cranial LV wall, but without concomitant functional changes. Increased myocyte size appears to be a more likely contributor to early LV thickening in response to high-fat feeding. These findings suggest that myocyte hypertrophy may be an early change leading to gross LV hypertrophy in the hearts of "healthy" obese rats, in the absence of hypertension, diabetes and myocardial ischemia.